1. Field of the Invention
The present invention relates to the field of data processing. More particularly, the invention relates to power supply detection circuitry for detecting when a supply voltage level has reached a predetermined voltage level.
2. Background to the Invention
In a data processing circuit, leakage current through the circuit contributes to the power consumed by the circuit, and so it may be desirable to reduce the amount of leakage current in order to reduce power consumption. One technique for reducing the leakage current is to gate the power supplied to the circuit block using power switches. The amount of leakage current is dependent on the voltage difference across the circuit. Hence, the processing circuit may be provided with a standby mode in which a given voltage difference is supplied to the circuit to enable processing operations to be performed, and a low leakage mode in which the voltage difference across the circuit is reduced to save leakage current but processing cannot be performed.
However, once the circuit has been placed in the low leakage mode, there will be a penalty in performance due to the time taken to switch the circuit back to the standby mode ready for the circuit to begin normal processing. When a power rail is switched from a low leakage supply level to an external supply level, then a ready signal may be generated when the power rails are within a specified range of the external supply rail to signal to the circuit that it can be reset and become operational. It is desirable to reduce the area overhead associated with generating the ready signal.